CN111480235B - Image sensor and manufacturing method thereof - Google Patents

Abstract

Some embodiments of the present application provide an image sensor and a manufacturing method thereof. The image sensor includes a substrate (400) and at least one pixel unit. The pixel unit includes a photodetector (401), which is disposed in the substrate. The photosensitive surface of the photodetector faces the back of the substrate, and is used to detect images from the back of the substrate. When incident light is received, charges are generated; a spherical cap-shaped structure (406) is provided on the substrate and is located opposite the photosensitive surface; a conformal dielectric layer (420) is provided above the spherical cap-shaped structure for incident light When light reaches the conformal dielectric layer, light reflected by the dielectric layer is generated; the reflective layer (430) is provided above the conformal dielectric layer and is used to generate reflected light from the reflective layer when the incident light reaches the reflective layer, so that the intensity of the incident light can be increased. The absorption ratio improves the signal quality of the image.

Description

Image sensor and manufacturing method

Technical field

The present application relates to the technical field of image sensors, and in particular to an image sensor and a manufacturing method thereof.

Background technique

CMOS image sensors are widely used in mobile phones, digital cameras, driving recorders, security monitoring and other equipment. Its working principle is based on the photoelectric conversion effect. When light illuminates the pixel array in the image sensor, each pixel unit generates a corresponding amount of charge according to the light intensity at its corresponding position, and converts it into a digital signal. Finally, all pixels The signal from the unit is processed and output as an image. According to structural classification, CMOS image sensors can be divided into front-illuminated image sensors and back-illuminated image sensors. Since the incident light of the back-illuminated image sensor directly illuminates the photosensitive area from the back, the responsivity of the back-illuminated image sensor is higher than that of the front-illuminated image sensor. The image sensor is higher.

The circuit diagram of a pixel unit of a common back-illuminated image sensor in the prior art, as shown in Figure 1, includes a photodiode 11 and four transistors 12, 14, 16 and 18, where the transmission transistor 12 controls the photodiode 11 Transfer of the generated charge to the floating diffusion node. The dotted frame area represents the schematic structure of the pixel unit structure 10. Refer to Figure 2. The silicon substrate 100 includes a photodiode 101, that is, the photodiode 11 in Figure 1, and a floating diffusion node 102, that is, Figure 2. 13 in 1, the gate structure 105 of the transmission transistor is provided on the silicon substrate 100, the incident light 140 irradiates the photodiode 101 from the back side of the silicon substrate 100 and generates charges.

The inventor found that the existing technology has at least the following problems: in recent years, new technologies such as AR/VR and 3D face recognition have continued to emerge, because these technologies mostly use near-infrared light that is invisible to the human eye as a light source (for example, using 940 nanometer VCSEL is used as a light source (Apple iPhoneX dot matrix projection module), so there is an increasing demand for image sensors with high responsiveness in near-infrared light. Compared with the visible light band, the absorption rate of near-infrared light in photodiodes is inherently low due to its longer wavelength; when the thickness of silicon is small, part of the near-infrared light will penetrate through the silicon, as shown in Figure 2 141 That is, light that cannot be absorbed but penetrates. Therefore, traditional back-illuminated image sensors have a problem of low absorption ratio of incident light, resulting in poor image signal quality.

Contents of the invention

The purpose of some embodiments of the present application is to provide an image sensor and a manufacturing method thereof, which can increase the absorption ratio of incident light by the image sensor and improve the signal quality of the image.

Embodiments of the present application provide an image sensor, including: a substrate and at least one pixel unit; the pixel unit includes a photodetector, which is disposed in the substrate, and the photosensitive surface of the photodetector faces the back of the substrate, used to generate charges when incident light is received from the back side of the substrate; a spherical cap-shaped structure, which is disposed on the substrate and located on the opposite surface of the photosensitive surface; a conformal dielectric layer, which is disposed on the spherical cap-shaped structure The upper part is used to generate light reflected by the medium layer when the incident light reaches the conformal dielectric layer; the reflective layer is arranged above the conformal dielectric layer and is used to generate light reflected by the reflective layer when the incident light reaches the reflective layer.

Embodiments of the present application also provide a method for manufacturing an image sensor, which includes: providing a substrate, forming a photodetector in the substrate, with the photosensitive surface of the photodetector facing the back of the substrate; A spherical cap-shaped structure is formed on the opposite surface of the photosensitive surface of the photodetector; a conformal dielectric layer is formed on the spherical cap-shaped structure; and a reflective layer is formed above the conformal dielectric layer.

Compared with the existing technology, the embodiment of the present application is that the pixel unit of the image sensor is provided with a spherical cap-shaped structure on the opposite surface of the photosensitive surface of the photodetector, and a conformal dielectric layer is provided above the spherical cap-shaped structure for When the incident light reaches the conformal dielectric layer, light reflected by the dielectric layer is generated. The spherical cap-shaped structure and the conformal dielectric layer ensure that when the incident light is incident at any angle, the optical path from entering the photodetector to passing through the substrate and reaching the conformal dielectric layer is the same. The medium generated when the incident light reaches the conformal dielectric layer The layer reflected light can give the incident light that penetrates the substrate a chance to return to the photodetector again, thereby increasing the absorption of incident light at different incident angles. For the incident light penetrating the conformal dielectric layer, the reflective layer disposed above the conformal dielectric layer is used to generate the reflected light of the reflective layer, so that the incident light reaching the reflective layer has the opportunity to return to the photodetector again, so that the photodetector can fully Incident light incident at different incident angles is utilized to increase the absorption ratio of incident light and improve the signal quality of the image.

For example, the conformal dielectric layer specifically includes: multiple conformal dielectric layers; wherein the refractive index of two adjacent conformal dielectric layers is different. That is to say, the conformal dielectric layer can adopt a structure in which dielectric materials with different refractive indexes are alternately stacked, which is conducive to further increasing the light absorption ratio.

In some embodiments, the multi-layer conformal dielectric layer specifically includes: three conformal dielectric layers; wherein the three conformal dielectric layers are respectively: a first silicon dioxide dielectric layer located on the spherical cap-shaped structure; a titanium dioxide dielectric layer on a silicon dioxide dielectric layer; and a second silicon dioxide dielectric layer on the titanium dioxide dielectric layer.

In some embodiments, the conformal dielectric layer has a preset thickness that satisfies the optical resonance condition of incident light. By controlling the thickness of the conformal dielectric layer to meet the optical resonance conditions of the incident light, the incident light at different angles can achieve optical resonance in the same structure, which is conducive to maximizing the use of the incident light.

In some embodiments, the phase θ of the light reflected by the dielectric layer and the phase θ of the light reflected by the reflective layer Specifically calculated through the following formula:

Among them, d is the preset thickness of the conformal dielectric layer, n _d is the refractive index of the conformal dielectric layer, λ is the wavelength of the incident light; n _r is the refractive index of the reflective layer, k _r is the extinction coefficient of the reflective layer, providing a kind of θ and The calculation formula is helpful for accurately passing θ and/> The relationship between them results in the preset thickness of the conformal dielectric layer.

In some embodiments, a spherical cap-shaped structure, specifically a spherical cap-shaped silicon structure, provides a material type of the spherical cap-shaped structure.

In some embodiments, the incident light is specifically: near-infrared monochromatic light. In a scenario where near-infrared monochromatic light invisible to the human eye is used as the light source, the absorption ratio of near-infrared monochromatic light is optimized, which is helpful to Improve the responsivity of the image sensor in the near-infrared band.

Description of the drawings

One or more embodiments are exemplified by the pictures in the corresponding drawings. These illustrative illustrations do not constitute limitations to the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements. Unless otherwise stated, the figures in the drawings are not intended to be limited to scale.

1 is a circuit diagram of a pixel unit of a back-illuminated image sensor according to the background technology of the present application;

Figure 2 is a schematic structural diagram of a pixel unit of a back-illuminated image sensor according to the background technology of the present application;

Figure 3 is a schematic diagram of the silicon layer-single conformal dielectric layer-reflective layer used in the image sensor according to the first embodiment of the present application;

Figure 4 is a schematic diagram of the pixel unit structure of the image sensor according to the first embodiment of the present application;

Figure 5 is a curve of the absorption ratio of the photodetector for incident light with a wavelength of 940 nm as a function of the thickness of the silicon dioxide dielectric layer according to the second embodiment of the present application;

Figure 6 is a schematic diagram of a pixel unit structure of an image sensor according to a third embodiment of the present application;

Figure 7 is a curve of the light absorption ratio of the photodetector according to the third embodiment of the present application as a function of the wavelength of the incident light;

Figure 8 is a flow chart of a manufacturing method of an image sensor according to a fourth embodiment of the present application;

Figures 9a to 9f are structural schematic diagrams of each step of the process flow in the fourth embodiment of the present application;

FIG. 10 is a flow chart of a manufacturing method of an image sensor according to the fifth embodiment of the present application.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application more clear, some embodiments of the present application are further described in detail below in conjunction with the drawings and examples. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application. The division of the following embodiments is for convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with each other and quoted from each other on the premise that there is no contradiction.

The first embodiment of the present application relates to an image sensor, including: a substrate, and at least one pixel unit; a photodetector, which is disposed in the substrate, with the light-sensitive surface of the photodetector facing the back of the substrate, and is used to detect light from the substrate When the back side of the bottom receives incident light, charges are generated; a spherical cap-shaped structure is provided on the substrate and is located on the opposite surface of the photosensitive surface; the spherical cap-shaped structure is made of the same material as the substrate; the conformal dielectric layer, The reflective layer is arranged above the spherical cap-shaped structure and is used to generate reflected light from the medium layer when the incident light reaches the conformal dielectric layer; the reflective layer is arranged above the conformal dielectric layer and is used to generate the reflective layer when the incident light reaches the reflective layer. Reflected light can increase the absorption ratio of incident light and improve the signal quality of the image. The implementation details of the pixel unit structure of the image sensor of this embodiment are described in detail below. The following content is only provided for the convenience of understanding and is not necessary for implementation of this solution.

In this embodiment, the conformal dielectric layer in the image sensor takes a single conformal dielectric layer as an example, but it is not limited to this in practical applications. In order to facilitate the understanding of this embodiment, a detailed description will be given first based on Figure 3. It should be noted that Figure 3 is for the convenience of illustrating the difference between the spherical cap-shaped structure 300, the single-layer conformal dielectric layer 320 and the reflective layer 330. The reflected light does not reflect the shape structure of the spherical cap-shaped structure 300, the single-layer conformal dielectric layer 320 and the reflective layer 330. Among them, the spherical cap-shaped structure in this embodiment takes a silicon layer as an example. The single-layer conformal dielectric layer can be a silicon dioxide dielectric layer, a titanium dioxide dielectric layer, etc., and the reflective layer is generally made of metals such as aluminum and silver.

Specifically, as shown in Figure 3, a vertically incident single-wavelength incident light 340 generates reflected light 341 when it reaches the interface 301 between the air 350 and the silicon layer; when the incident light reaches the silicon layer and the single-layer conformal Reflected light 342 is generated when the interface 310 of the dielectric layer 320 is reached; reflected light 343 is generated when the incident light reaches the interface 325 of the single-layer conformal dielectric layer 320 and the reflective layer 330 .

Further, the image sensor in this embodiment includes a substrate 400 and a pixel unit structure as shown in Figure 4, including: photodetector 401, floating diffusion node 402, shallow trench isolation 403, gate dielectric layer 404 , the gate structure 405 of the transmission transistor, the spherical crown structure 406, the interlayer dielectric layer 410, the single-layer conformal dielectric layer 420 and the reflective layer 430.

Specifically, the substrate 400 may be a silicon substrate, and the silicon substrate has a front side and a back side. In FIG. 4 , the direction of the upward arrow is the back side, and the direction of the downward arrow is the front side.

Specifically, the photodetector 401 is disposed in the substrate 400. The photosensitive surface of the photodetector 401 faces the back of the substrate 400, and is used to generate charges when receiving incident light from the back of the substrate 400. It can be incident at any incident angle, such as vertically incident incident light 440 and non-normally incident incident light 450 in Figure 4 , where the photodetector 401 in this embodiment can be a photodiode.

Furthermore, as new technologies such as AR/VR and 3D face recognition continue to emerge, since these technologies mostly use near-infrared light that is invisible to the human eye as a light source, image sensors with high responsiveness to near-infrared light are required. The demand for it is increasing day by day. Compared with the visible light band, the absorption rate of near-infrared light in photodetectors is inherently low due to its longer wavelength. When the thickness of silicon is thin, part of the near-infrared light will penetrate from the silicon. , which is not conducive to the utilization of light. The pixel unit structure of the image sensor in this embodiment allows the near-infrared light incident at different angles that penetrates the silicon layer to have the opportunity to return to the photodetector again, thereby increasing light absorption. In other words, if the incident light is near-infrared monochromatic light with a wavelength of 780 to 1100 nm, in application scenarios where a laser with good monochromaticity is used as a near-infrared light source, it will help to improve the performance of the image sensor in the near-infrared band. responsiveness.

Specifically, the floating diffusion node 402 is disposed in the substrate 400 for storing received charges and converting the stored charges into voltage signals.

Specifically, shallow trench isolation 403 is provided on both sides of the substrate 400 to isolate interference from adjacent pixel unit structures.

Specifically, the gate structure 405 of the transmission transistor is provided on the gate dielectric layer 404, and the gate dielectric layer 404 is provided on the substrate 400. The transmission transistor is used to control the charge generated by the photodetector 401 to the floating diffusion node. 402 transmission, the gate structure 405 can be used as a switch to control charge transmission, controlling whether to start or stop transmitting charge. The gate structure of the pass transistor 12 in FIG. 1 is the gate structure 405 of the pass transistor in FIG. 4 .

Specifically, the spherical cap-shaped structure 406 can be a spherical cap-shaped structure with a radius of curvature R. The spherical cap-shaped structure 406 and the substrate 400 are made of the same material. For example, the material used can be a common semiconductor material. Preferably, in this embodiment, the substrate is a silicon substrate and the spherical cap-shaped structure is a spherical cap-shaped silicon structure. However, in practical applications, it is not limited to this. The spherical cap-shaped silicon structure is disposed on the substrate 400 and is located opposite the light-sensitive surface of the photodetector 401 .

Specifically, the single-layer conformal dielectric layer 420 is disposed above the spherical cap-shaped structure 406 to generate reflected light from the dielectric layer when the incident light reaches the single-layer conformal dielectric layer 420. The single-layer conformal dielectric layer 420 can Has a certain thickness.

Specifically, the reflective layer 430 is disposed above the single-layer conformal dielectric layer 420, and is used to generate light reflected by the reflective layer when incident light reaches the reflective layer 430.

It can be seen from the above pixel unit structure that whether the incident light 440 is vertically incident or the incident light 450 is not vertically incident, the optical path to the reflective layer 430 is the same.

Compared with the existing technology, this embodiment forms a spherical crown-shaped silicon structure with a specific curvature radius in the area above the image opposite side of the photosensitive surface of the photodetector, and then forms a single layer with a specific thickness on the spherical crown-shaped silicon structure. The conformal dielectric layer and the reflective layer, through the pixel unit structure in this embodiment, allow the incident light that penetrates the silicon layer to have the opportunity to return to the photodetector again, thereby increasing the absorption of light. Moreover, it can also ensure that the optical path of incident light at different angles is the same, thus optimizing the absorption ratio of incident light at different angles in the photodetector.

The second embodiment of the present application relates to an image sensor. In this embodiment: the conformal dielectric layer has a preset thickness, and the preset thickness satisfies the optical resonance condition. The optical resonance effect is used to maximize the reflectivity, further increasing the incident light. The ratio of light absorption.

Specifically, the optical resonance condition is that the phase difference between the reflected light 342 and the reflected light 343 in Figure 3 is zero or an integer multiple of 2π, that is, a standing wave is formed. There are two sources of the above-mentioned phase difference: one is the phase change θ caused by the thickness d of the single-layer conformal dielectric layer 320, as shown in the following formula (1):

The second is the phase change φ caused by the light absorption of the reflective layer 330 at the interface 325 of the reflective layer 330, as shown in the following formula (2):

Among them, _nd is the refractive index of the single-layer conformal dielectric layer 320, n _r and k _r are the refractive index and extinction coefficient of the reflective layer 330 respectively, and λ is the wavelength of the incident light. The condition for forming a standing wave is that the phase difference between reflected light 342 and reflected light 343 satisfies the following formula (3), where N is a natural number:

Furthermore, it can be seen from the above formulas (1) to (3) that for incident light incident at different angles, the thickness d of the single-layer conformal dielectric layer 320 only needs to meet specific conditions to satisfy the resonance conditions of the light, so that Greatly increases the proportion of light absorption.

In one example, as shown in Figure 4, the single-layer conformal dielectric layer 420 can be a conformal silicon dioxide dielectric layer with a thickness of _dSiO2 . The radius of curvature of the spherical cap-shaped structure 406 is R=2215 nanometers. The incident light The wavelength is 940 nanometers. The absorption ratio of the incident light in silicon changes with the thickness of the silicon dioxide dielectric layer as shown in Figure 5. According to formula (3), it can be calculated that when d _SiO2 = 144.9 nanometers, 468.8 nanometers or 792.6 nanometers, the optical resonance conditions can be met. At this time, the corresponding maximum value of the absorption ratio is 38.5%. In addition, it can be seen from FIG. 5 that without the silicon dioxide dielectric layer, the absorption ratio is only 5%. That is, the single-layer conformal dielectric layer 420 provided in this embodiment is beneficial to increasing the absorption ratio of incident light. It should be noted that the single-layer conformal dielectric layer in this embodiment is only a conformal silicon dioxide dielectric layer as an example, and is not limited to this in practical applications. It should be noted that "conformal" as used herein means maintaining the same shape as a certain structure. For example, the conformal dielectric layer maintains the same shape as a spherical cap-shaped silicon structure.

Compared with the existing technology, this embodiment has a preset thickness of the conformal dielectric layer. The preset thickness meets the optical resonance conditions of the incident light, which allows the incident light incident at different angles to pass through the spherical cap-shaped silicon structure and the conformal medium. Both the first layer and the reflective layer can form optical resonance, which optimizes the absorption ratio of incident light and is conducive to maximizing the use of incident light. Moreover, by using the pixel structural unit in this embodiment, the same structure can be used to make the incident light incident at different angles meet the conditions of optical resonance. At the same time, we get θ and The calculation formula is helpful for accurately passing θ and/> The relationship between them results in the preset thickness of the conformal dielectric layer.

The third embodiment of the present application relates to an image sensor. This embodiment is substantially the same as the second embodiment. The difference is that in the second embodiment, the conformal dielectric layer is specifically a single-layer conformal dielectric layer, while in this embodiment , the conformal dielectric layer is specifically a multi-layer conformal dielectric layer, which provides an implementation method of the conformal dielectric layer.

In the multi-layer conformal dielectric layer in the pixel unit structure of the image sensor in this embodiment, the refractive index of two adjacent conformal dielectric layers is different. That is to say, the conformal dielectric layer can adopt a structure in which dielectric materials with different refractive indexes are alternately stacked. The following is an example of three layers of conformal dielectric layers. However, in practical applications, it is not limited to three layers. The pixel unit structure of the image sensor of the conformal dielectric layer can be shown in Figure 6.

Specifically, the three conformal dielectric layers can be respectively: the first silicon dioxide dielectric layer 620 located on the spherical crown structure; the titanium dioxide dielectric layer 621 located on the first silicon dioxide dielectric layer 620; and, the titanium dioxide dielectric layer 621 located on the titanium dioxide dielectric layer 620. A second silicon dioxide dielectric layer 622 on the dielectric layer 621 . Among them, the refractive index of silicon dioxide is 1.45, which is a low-refractive index material; the refractive index of titanium dioxide is 2.25, which is a high-refractive index material. The use of this structure in which high and low refractive index materials are alternately stacked is conducive to further increasing the proportion of light absorption. . It should be noted that in this embodiment, silicon dioxide and titanium dioxide are used as examples of different dielectric materials, but they are not limited to this in practical applications.

Further, the thickness of each layer of dielectric material meets the optical resonance conditions of monochromatic light of a specific wavelength. According to the resonance conditions of light, it can be calculated that when the thickness of the first silicon dioxide dielectric layer 620 is 485.8 nanometers, the thickness of the titanium dioxide layer dielectric layer is 104.5 nanometers, and the thickness of the second silicon dioxide dielectric layer is 144.9 nanometers, it can be satisfied Optical resonance conditions for monochromatic light with a wavelength of 940 nm. As shown in Figure 7, the light absorption ratio of the photodetector changes with the wavelength of the incident light. At this time, the light absorption ratio reaches a maximum value of 40.5%.

Compared with the existing technology, the conformal dielectric layer in this embodiment is specifically: multiple conformal dielectric layers; wherein the refractive index of two adjacent conformal dielectric layers is different. That is to say, the conformal dielectric layer can adopt a structure in which dielectric materials with different refractive indexes are alternately stacked, which is conducive to further increasing the light absorption ratio.

The fourth embodiment of the present application relates to a method for manufacturing a pixel unit structure of an image sensor, which includes: providing a substrate, forming a photodetector in the substrate, with the photosensitive surface of the photodetector facing the back of the substrate; A spherical cap-shaped structure is formed on the bottom and opposite to the photosensitive surface of the photodetector; wherein the spherical cap-shaped structure is made of the same material as the substrate; a conformal dielectric layer is formed on the spherical cap-shaped structure; on the conformal dielectric layer A reflective layer is formed above, so that a pixel unit structure like the image sensor in the first embodiment can be manufactured. The implementation details of the manufacturing method of the pixel unit structure of the image sensor of this embodiment are described in detail below. The following content is only implementation details provided for convenience of understanding and is not necessary for implementation of this solution.

In the manufacturing method of the image sensor in this embodiment, the prepared conformal dielectric layer of the pixel unit structure is a single layer of conformal dielectric layer, that is, the prepared pixels of the image sensor in the first embodiment or the second embodiment are unit structure. The specific flow chart of the manufacturing method is shown in Figure 8, including:

Step 801: Provide a substrate, and form shallow trench insulation on the substrate.

Specifically, referring to FIG. 9a, shallow trench insulation 901 is formed on both sides of the substrate 900 to isolate interference from adjacent pixels.

Step 802: Form a spherical cap-shaped structure on the substrate and on the surface opposite to the photosensitive surface of the photodetector.

Specifically, the spherical cap-shaped silicon structure is a type of spherical cap-shaped structure. The spherical cap-shaped structure is made of the same material as the substrate. The substrate in this embodiment is a silicon substrate as an example. The spherical cap-shaped structure is made of a spherical cap-shaped silicon structure. The silicon-shaped structure is used as an example, but in practical applications, it is not limited to this. Specifically, a spherical cap-shaped photoresist can be formed first through a photoresist reflow or grayscale mask exposure process, and then the spherical cap-shaped photoresist can be transferred to the substrate 900 through reactive ion etching. , please refer to Figure 9b, in which a spherical crown-shaped silicon structure 904 is formed above the photodetector 903 area. The photodetector 903 in this embodiment may be a photodiode, and the photodiode is disposed in the substrate 900 .

Step 803: Form an ion doped region, a gate, a first interlayer dielectric layer and other structures on the substrate.

Specifically, referring to Figure 9c, the ion doped region formed in the substrate may include: a photodetector 903, a floating diffusion node 906, etc., and a gate dielectric layer 907, a gate structure 908 and a first Interlayer dielectric layer 910 and other structures.

Step 804: Remove the first interlayer dielectric layer on the opposite surface of the photosensitive surface of the photodetector to expose the spherical cap-shaped silicon structure.

Specifically, referring to FIG. 9d , the first interlayer dielectric layer 910 above the photodetector 903 area is removed to expose the spherical cap-shaped silicon structure 904.

Step 805: Form a conformal dielectric layer on the spherical cap-shaped silicon structure and form a reflective layer above the conformal dielectric layer.

Specifically, referring to FIG. 9e, a conformal dielectric layer 920 and a reflective layer 930 of a specific thickness are formed on the spherical cap-shaped silicon structure 904, and then a second interlayer dielectric layer 940 is deposited and planarized. Preferably, the conformal dielectric layer 920 can have a preset thickness, and the preset thickness can meet the optical resonance conditions. The content of the optical resonance conditions has been introduced in detail in the second embodiment. Please refer to the description in the second embodiment. , this embodiment will not be repeated here to avoid repetition.

It should be noted that after the second interlayer dielectric layer 940 is deposited and planarized, the remaining process can be completed according to the standard image sensor process flow. Refer to FIG. 9f, including conductive vias 911, metal interconnection lines 912 and inter-metal The production of the dielectric layer 915, the bonding with the carrier wafer 950, the thinning of the backside of the substrate 900, the production of the anti-reflection layer 960 and the microlens 970, etc. Since these are all standard processes for image sensors, they will not be described in detail here.

The fifth embodiment of the present application relates to a manufacturing method of an image sensor. This embodiment is substantially the same as the fourth embodiment, except that the conformal dielectric layer in the pixel unit structure of the image sensor prepared in the fourth embodiment is a single layer, while the conformal dielectric layer in the pixel unit structure of the image sensor prepared in this embodiment is multi-layer, that is, this embodiment provides a method for preparing the pixel unit structure of the image sensor in the third embodiment. .

The specific flow chart of the manufacturing method of the image sensor in this embodiment is shown in Figure 10, which specifically includes:

Step 1001: Provide a substrate, and form shallow trench insulation on the substrate.

Step 1002: Form a spherical cap-shaped structure on the substrate and on the surface opposite to the photosensitive surface of the photodetector.

Step 1003: Form an ion doped region, a gate, a first interlayer dielectric layer and other structures on the substrate.

Step 1004: Remove the first interlayer dielectric layer on the opposite surface of the photosensitive surface of the photodetector to expose the spherical cap-shaped silicon structure.

Steps 1001 to 1004 are substantially the same as steps 901 to 904 in the fourth embodiment, and will not be repeated here to avoid repetition.

Step 1005: Form two or more conformal dielectric layers of specific thickness on the spherical cap-shaped silicon structure and form a reflective layer above the conformal dielectric layer.

Specifically, two or more conformal dielectric layers are an alternating stack structure of high and low refractive index materials. The following takes three layers of conformal dielectric layers as an example. First, the thickness of the conformal dielectric layers of three different dielectric materials can be obtained according to the resonance conditions of light. When forming three conformal dielectric layers with a specific thickness, a first silicon dioxide dielectric layer can be formed on the spherical cap-shaped silicon structure; then a titanium dioxide dielectric layer can be formed on the first silicon dioxide dielectric layer; and then, A second silicon dioxide dielectric layer is formed on the titanium dioxide dielectric layer, so that a three-layer conformal dielectric layer stack structure is finally formed. Finally, a reflective layer is formed on the second silicon dioxide dielectric layer. It should be noted that in this embodiment, silicon dioxide and titanium dioxide are used as examples of different dielectric materials, but they are not limited to this in practical applications.

It should be noted that after step 1005, the remaining processes can be completed according to the process flow of a standard image sensor by referring to the steps after step 905 in the fourth embodiment. To avoid duplication, the details are not repeated here.

It should be understood that the above method takes a single pixel structure as the description object, and the corresponding boundaries of the substrate 900 shown in Figures 9a-9f are not the real boundaries of the substrate.

The steps of the various methods above are divided just for the purpose of clear description. During implementation, they can be combined into one step or some steps can be split into multiple steps. As long as they include the same logical relationship, they are all within the scope of protection of this patent. ; Adding insignificant modifications or introducing insignificant designs to the algorithm or process without changing the core design of the algorithm and process are within the scope of protection of this patent.

Those of ordinary skill in the art can understand that the above-mentioned embodiments are specific embodiments for implementing the present application, and in actual applications, various changes can be made in form and details without departing from the spirit and spirit of the present application. scope.

Claims (19)

1. An image sensor, comprising a substrate and at least one pixel unit, characterized in that the pixel unit includes: A photodetector, disposed in the substrate, with the photosensitive surface facing the back of the substrate, for generating charge when receiving incident light from the back of the substrate; A spherical cap-shaped structure, arranged on the substrate and located on the opposite surface of the photosensitive surface; A conformal dielectric layer, disposed above the spherical cap-shaped structure, used to generate reflected light from the dielectric layer when the incident light reaches the conformal dielectric layer; and A reflective layer, disposed above the conformal dielectric layer, is used to generate reflected light from the reflective layer when the incident light reaches the reflective layer; the conformal dielectric layer has a preset thickness, and the preset thickness satisfies The optical resonance condition of the incident light; the optical resonance condition is: the phase θ of the light reflected by the dielectric layer and the phase φ of the light reflected by the reflective layer satisfy the following formula: Wherein, N is a natural number. 2. The image sensor according to claim 1, wherein the conformal dielectric layer is a multi-layer conformal dielectric layer; wherein two adjacent conformal dielectric layers have different refractive indexes. 3. The image sensor according to claim 2, wherein the multiple conformal dielectric layers are three conformal dielectric layers; wherein the three conformal dielectric layers are respectively: a first silicon dioxide dielectric layer located on the spherical cap-shaped structure; a titanium dioxide dielectric layer located on the first silicon dioxide dielectric layer; and, a second silicon dioxide dielectric layer located on the titanium dioxide dielectric layer. 4. The image sensor according to claim 1, characterized in that the phase θ of the light reflected by the dielectric layer and the phase of the light reflected by the reflective layer Specifically calculated through the following formula: Wherein, d is the preset thickness of the conformal dielectric layer, n _d is the refractive index of the conformal dielectric layer, λ is the wavelength of the incident light; n _r is the The refractive index of the reflective layer, and k _r is the extinction coefficient of the reflective layer. 5. The image sensor according to claim 1, wherein the spherical cap-shaped structure is a spherical cap-shaped silicon structure. 6. The image sensor according to claim 1, further comprising: The gate structure of the transmission transistor is provided on the gate dielectric layer, and the gate dielectric layer is provided on the substrate. The transmission transistor is used to control the transmission of charges generated by the photodetector to the floating diffusion node. , the gate structure is a switch that controls charge transfer; The floating diffusion node is disposed in the substrate and is used to store received charges and convert the stored charges into voltage signals. 7. The image sensor according to claim 1, further comprising: Shallow trench isolation is provided on both sides of the substrate to isolate interference from adjacent pixel unit structures. 8. The image sensor according to claim 1, wherein the incident light is near-infrared monochromatic light. 9. The image sensor according to any one of claims 1 to 8, wherein the spherical cap-shaped structure is made of the same material as the substrate. 10. The image sensor according to any one of claims 1-8, wherein the photodetector is a photodiode. 11. A method of manufacturing an image sensor, characterized by comprising: Provide a substrate, form a photodetector in the substrate, and the light-sensitive surface of the photodetector faces the back of the substrate; A spherical cap-shaped structure is formed on the substrate and on the surface opposite to the photosensitive surface of the photodetector; wherein the spherical cap-shaped structure is made of the same material as the substrate; forming a conformal dielectric layer on the spherical cap-shaped structure; A reflective layer is formed above the conformal dielectric layer; the conformal dielectric layer has a preset thickness, and the preset thickness satisfies the optical resonance condition of the incident light; the optical resonance condition is: the phase θ of the light reflected by the dielectric layer and the phase of light reflected from the reflective layer Satisfy the following formula:/> Wherein, the reflected light of the dielectric layer is the reflected light of the preset monochromatic light by the conformal dielectric layer, the reflected light of the reflective layer is the reflected light of the preset monochromatic light by the reflective layer, and the N is a natural number. 12. The method for manufacturing an image sensor according to claim 11, wherein forming a spherical cap-shaped structure on the substrate and on a surface opposite the light-sensitive surface of the photodetector specifically includes: Through photoresist reflow or grayscale mask exposure process, a spherical cap-shaped photoresist is formed; Transferring the spherical cap-shaped photoresist into the substrate through reactive ion etching; forming a first interlayer dielectric layer on the substrate; The first interlayer dielectric layer located in the area above the opposite surface of the photosensitive surface of the photodetector is removed to expose the spherical cap-shaped structure. 13. The manufacturing method of the image sensor according to claim 12, characterized in that after forming a reflective layer above the conformal dielectric layer, it further includes: A second interlayer dielectric layer is deposited on the reflective layer and planarized. 14. The manufacturing method of the image sensor according to claim 11, characterized in that after forming the photodetector in the substrate, it further includes: A floating diffusion node is formed within the substrate, and a gate structure of a pass transistor is formed on the substrate. 15. The manufacturing method of the image sensor according to claim 11, characterized in that, before forming the photodetector in the substrate, further comprising: Shallow trench isolation is formed on both sides of the substrate. 16. The method of manufacturing an image sensor according to claim 11, wherein the conformal dielectric layer is a multi-layer conformal dielectric layer; wherein two adjacent conformal dielectric layers have different refractive indexes. 17. The manufacturing method of the image sensor according to claim 16, wherein the multiple conformal dielectric layers are three conformal dielectric layers; wherein the three conformal dielectric layers are respectively: a first silicon dioxide dielectric layer located on the spherical cap-shaped structure; a titanium dioxide dielectric layer located on the first silicon dioxide dielectric layer; and, a second silicon dioxide dielectric layer located on the titanium dioxide dielectric layer. 18. The manufacturing method of the image sensor according to claim 11, characterized in that the phase θ of the light reflected by the dielectric layer and the phase of the light reflected by the reflective layer Specifically calculated through the following formula: Wherein, the n _d is the refractive index of the dielectric layer, the λ is the wavelength of the incident light; the n _r is the refractive index of the reflective layer, and k _r is the extinction of the reflective layer. coefficient. 19. The method of manufacturing an image sensor according to claim 11, wherein the spherical cap-shaped structure is a spherical cap-shaped silicon structure.